1. Field Of The Invention
The present invention relates to cementing head apparatus, and more particularly, to a cementing head having a plug container body rotatable with respect to a cementing manifold while maintaining fluid communication therebetween. This allows simultaneous rotation from above and reciprocation of the cementing head while pumping to improve cement flow through the apparatus and drill string or casing attached thereto.
2. Description Of The Prior Art
One type of cementing apparatus which is commonly used in the completion of offshore wells is that known as a subsurface release cementing system. In a subsurface release cementing system, cement plugs are hung off in the upper end of the casing near the ocean floor. Devices such as balls and darts are released from a plug container or cementing head located at the floating drilling rig. The balls or darts fall downwardly through the drill pipe to engage the cementing plugs hung off in the casing head and to cause those cementing plugs to be released so that they will then flow downwardly through the casing with the cement.
One such system is shown in U.S. Pat. No. 4,624,312 to McMullin, assigned to the assignee of the present invention. These types of cementing plug methods and equipment are also described in Halliburton Sales & Service Catalog No. 43 (1985), pages 2423-2426. In this apparatus there is a cementing manifold attached to the plug container above and below the top releasing plug and plug release.
It is known to construct the cementing head in what is known as a "lift-through" design, wherein the entire weight of the drill pipe string hung below the drilling platform is supported through or lifted through the structure of the cementing head. This allows the plug container and drill pipe string to be reciprocated during cementing operations to help remove mud from the well annulus and provide an even distribution of cement in the annulus. This reciprocation is accomplished by attaching the rig elevators to the apparatus so that the cementing head and drill string may be reciprocated by the elevators.
While reciprocation of the apparatus during cementing has the advantages mentioned, rotation of the casing also helps provide better cement flow. A problem with the prior art cementing heads described above is that the cementing manifold is rigidly connected to the plug container body so that rotation of the body is prevented because of the cementing lines connected to the cementing manifold. Thus, the only way to rotate the casing was to disconnect the cementing lines prior to rotation. In other words, rotation could not occur while cement was actually being pumped.
Lift-through cementing heads have been developed with swivel connections between the plug container body and the drill pipe string therebelow. One such apparatus is disclosed in U.S. patent application Ser. No. 07/444,657, now U.S. Pat. No. 4,995,457 assigned to the assignee of the present invention. By engaging the drill pipe string below the swivel by the slips on the rig floor, rotation is possible without disconnecting the cementing lines from the cementing manifold. Thus, cement can be pumped through the apparatus and down the drill pipe string while the drill pipe string is rotated. However, the apparatus may not be reciprocated and rotated at the same time since the rotation is provided by the slips on the rig floor below the cementing head.
Accordingly, there is a need for a cementing head which may be both reciprocated and rotated simultaneously with the pumping of cement through the apparatus and down the drill pipe string. The present invention meets this need by providing a cementing head with a plug container body which may be rotated with respect to the cementing manifold while maintaining fluid communication therebetween so that cement may be pumped during rotation. With the present invention, rotation may be provided by top drive units above the apparatus which may be rotated substantially simultaneously with reciprocation by the elevators. Thus, the cementing head of the present apparatus may be reciprocated and rotated during a cement pumping operation.